Re: [spring] Request comments/feedback on https://datatracker.ietf.org/doc/draft-zzhang-spring-microtap-segment/01/

Hi,

  *   Also, the processing description seems to say taht the copy is made before the microTAP sid is removed.  Which seems to mean that the microtap SID will be the topmost SID in the copy and be the basis for forwarding?
Actually, for both MPLS and SRv6, the tapped copy should use the node SID of the owner of the microtap SID to get to the owner node (who advertised the microtap SID).

Jeffrey

Juniper Business Use Only
From: Gurminderjit Bajwa <gurminderjit.bajwa=40telus.com@dmarc.ietf.org>
Sent: Wednesday, March 13, 2024 4:41 PM
To: Joel Halpern <jmh@joelhalpern.com>
Cc: Jeffrey (Zhaohui) Zhang <zzhang@juniper.net>; spring@ietf.org; draft-zzhang-spring-microtap-segment@ietf.org
Subject: Re: [spring] Request comments/feedback on https://datatracker.ietf.org/doc/draft-zzhang-spring-microtap-segment/01/

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Hello Joel,

Please see comments below.

In the case of SR-MPLS, will the micro-tap SID come from the block associated with the processing node?  If so, how do we avoid collision between the microtap SID and the node's own SIDs?

[GB] In the case of SR-MPLS, the microTap SID is allocated from the SRGB which makes it globally unique and helps avoid collision with any node SIDs.

In the case of SRv6, it appears that the microTap SID will be an IPv6 address that is not advertisedby the node, and is in fact advertised by other nodes.  This seems to violate the rules for when a node processes a SID in the SRv6 specifications?

[GB] In the case of SRv6, microTap SID is advertised by the monitor node (i.e. a node connected to a monitor). Any node in the network that encounters the microTap SID would make a copy of the packet and send it to the monitor node. Does that answer your question?

Also, the processing description seems to say taht the copy is made before the microTAP sid is removed.  Which seems to mean that the microtap SID will be the topmost SID in the copy and be the basis for forwarding?
[GB] That is the case for SRv6.

Thanks,
Gurminder

On Fri, Mar 1, 2024 at 1:25 PM Joel Halpern <jmh@joelhalpern.com<mailto:jmh@joelhalpern.com>> wrote:

Looking at this draft, I am trying (as a participant) to understand the SIDs as they will appear in packets.

In the case of SR-MPLS, will the micro-tap SID come from the block associated with the processing node?  If so, how do we avoid collision between the microtap SID and the node's own SIDs?

In the case of SRv6, it appears that the microTap SID will be an IPv6 address that is not advertisedby the node, and is in fact advertised by other nodes.  This seems to violate the rules for when a node processes a SID in the SRv6 specifications?

Also, the processing description seems to say taht the copy is made before the microTAP sid is removed.  Which seems to mean that the microtap SID will be the topmost SID in the copy and be the basis for forwarding?

Yours,

Joel
On 3/1/2024 11:51 AM, Jeffrey (Zhaohui) Zhang wrote:
Hi Ed, Jeff,

Thanks for your comments.
Please see zzh> below.

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Cc: Ryan Hoffman <ryan.hoffman=40telus.com@dmarc.ietf.org><mailto:ryan.hoffman=40telus.com@dmarc.ietf.org>; Jeffrey (Zhaohui) Zhang <zzhang@juniper.net><mailto:zzhang@juniper.net>; spring@ietf.org<mailto:spring@ietf.org>; draft-zzhang-spring-microtap-segment@ietf.org<mailto:draft-zzhang-spring-microtap-segment@ietf.org>
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I think this is a relevant use-case / feature.

Few comments after first read:
- For SRv6 the procedure may be slightly different, ie steer traffic via MicroTAP capable node or have MicroTAP as integrated capability of "default" forwarding (of capable nodes) and indicate the parameter - this is the approach in the current draft if I understand correctly.

Zzh> The microtap segment belongs to the node connected to the monitor, which is typically not in the path of most traffic. When a capable node in the normal traffic path encounters a microtap SID (which is not advertised by that node), it makes a copy and send the copy to the owner of the microtap SID (while continue to forward the original copy after removing the microtap SID).
Zzh> Therefore, it is not an integrated capability of “default” forwarding (of capable nodes).

- Section 2.3 describes that if a MicroTAP SID becomes the active on the a node not supporting the MicroTAP capability, the packet would be dropped. I wondered if this is correct? Wouldnt the packet be forwarded to the "monitor" node? This breaks the communication effectively, but not a drop at the node not supported MicroTAP.

Zzh> A node not supporting MicroTAP will not advertise its capability or install the forwarding state for MicroTAP SIDs (advertised by the nodes connected to the monitors).
Zzh> As a result, other nodes SHOULD NOT place a MicroTap SID after the node/adj SID for the incapable node. In the unlikely case if that happened, in the case of MPLS the packet will simply be dropped (there is no corresponding state). In the case of SRv6, there might not be a corresponding IPv6 route either and traffic will also be dropped. But if there is a less specific route covering that MicroTap SID, then it will be forwarded accordingly. We will add that clarification.

- In general, or least for intercept, one would be interested in both directions of a traffic stream (e.g to / from a specific IP). To address this, the MicroTAP SID would need to inserted on all relevant ingresses. And the monitor may receive packets from different MicroTAP capable nodes. This may have implications for the use of IOM header (e.g. to avoid duplicate sequence ids)

Zzh> A monitor is going to receive tapped packets from all over the places (it all depends on which packets carry the MicroTap SID and where in the SID list), but unless a MicroTap SID is repeated (in different places of the SID list) in the packet, the monitor will only receive one tapped copy for a particular packet. I also imagine that an ingress is likely coordinating with the monitor when it places the MicroTap SID, even though that’s outside the scope of this draft.
Zzh> Can you explain the implications for the use of IOM header?
Zzh> Thanks.
Zzh> Jeffrey

cheers,
  Eduard

On Wed, Feb 28, 2024 at 4:52 AM Jeff Tantsura <jefftant.ietf@gmail.com<mailto:jefftant.ietf@gmail.com>> wrote:
Seems like a very useful feature indeed.

Cheers,
Jeff

On Feb 27, 2024, at 07:15, Ryan Hoffman <ryan.hoffman=40telus.com@dmarc.ietf.org<mailto:40telus.com@dmarc.ietf.org>> wrote:

TELUS intends to deploy this microTap segment feature once available in vendor NOS after thorough testing in our lab.  We'd expedite TELUS testing and deployment when available from vendors, as this is a much needed feature in our network.

Thanks,
Ryan Hoffman

On Wed, Apr 5, 2023 at 3:28 PM Jeffrey (Zhaohui) Zhang <zzhang@juniper.net<mailto:zzhang@juniper.net>> wrote:
Hi,

The authors of this draft would like to get your feedback on this draft.

   This document specifies a microTap segment that can be used to
   instruct a transit node to make a copy of a segment-routed packet and
   deliver it to a specified node for the purpose of network monitoring,
   trouble shooting, or lawful intercept.

Due to the limit of Spring WG session time we have not been able to present it but we submitted slides before: https://datatracker.ietf.org/meeting/115/materials/slides-115-spring-slides-115-spring-microtap-segment-00<https://urldefense.com/v3/__https:/datatracker.ietf.org/meeting/115/materials/slides-115-spring-slides-115-spring-microtap-segment-00__;!!NEt6yMaO-gk!EKhg-4oZEfTFYJNmgp8IGr1V5a4BR45VWyFGE1yjXKX5wyy_b1J1I5V1a1TwceJBWn4B_S11vdYmbIo$>.

Thanks.
Jeffrey

Juniper Business Use Only
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